Triple chamber pacemakers typically include a ventricular electrode (generally a bipolar endocardial lead), and two atrial electrodes which are respectively implanted on each of the two atria and commonly connected to a corresponding single input port of the pacemaker. The common connection is typically a Y connector.
In a classic "bipolar electrode" the two conductive extremities, namely the distal and proximal terminals, are separated by only a few millimeters. In the atrial bipolar electrode for use in a double atrial triple chamber pacemaker in accordance with the present invention, however, the distal and proximal terminals are relatively spaced apart much further, e.g., a typical distance on the order of 5 cm, so that one electrode terminal is implanted in the right atrium and the other electrode terminal is implanted in the left atrium.
Triple chamber cardiac pacemakers have been used in a relatively satisfactory manner for some years. They are useful in connection with patients having indications presenting an "intra-atrial block" sinusal disorder, in which there is a deficient propagation of conduction (either insufficient or too long) from the right atrium to the left atrium.
Thus, if only one of the atria is stimulated (e.g., the right atrium, as in the classic situation of a "double chamber" pacemaker), the other atrium (e.g., the left atrium), which is not stimulated, would receive the depolarization wave coming from the stimulated atrium, if at all, after an excessively long period. In some cases, the period is longer than the atrial-ventricular delay (AV delay). Such a phenomenon can result in a contraction of ventricles occurring before the left atrium has finished draining, and, therefore, before the mistral valve has closed. This produces a counter-flow of blood from the ventricle to the left atrium and a diminution of the hemodynamic efficiency.
In addition, the electrical desynchronisation of the two atria favors the occurrence of tachyarrhythmia events.
Further, it has been recognized that the inter-atrial propagation delay period increases with the patient's effort. Therefore, the increase of the physiological activity of the patient apparently favors the risk of appearance of a such a syndrome.
The known triple chamber pacemakers operate by stimulating the left and right atria in a simultaneous manner. This is done to avoid the appearance or the persistence of the aforementioned phenomenon. Nevertheless, clinical studies have revealed the appearance of atrial tachyarrhythmia (AT) for some patients, notwithstanding such a systematic, simultaneous stimulation of the two atria. These AT, whose origin had not up until now been able to be identified, typically necessitated further treatment of patients by medication (for example, by administering a beta-blocking therapy). However, such medicinal treatments have a certain residual failure rate, such that a medicinal treatment is not always sufficient to prevent the appearance of recurrent AT in some patients. In addition, the treatment of the recurrent AT by medication is contraindicated absolutely in some patients.